1. Technical Field
The present invention relates to a wavelength conversion element for converting a wavelength using a second harmonic wave generating element, and a light source device, an image display device, and a monitor device using the wavelength conversion element.
2. Related Art
An image display device such as a projector irradiating a spatial light modulator such as a liquid crystal light valve or a digital micromirror device (DMD) with irradiation beams from a light source device to display an image has been used. A laser source device for emitting a laser beam is sometimes used as the light source device.
Some of such laser source devices are each provided with a laser emitting element such as a laser diode and a nonlinear optical element in order for generating a visible light beam. The nonlinear optical element is an element for expressing a nonlinear optical effect such as generation of an optical harmonic wave or an optical parametric effect by light and a material causing a vary strong interaction. The wavelength conversion element is an element utilizing the optical harmonic wave generation effect out of the above nonlinear optical effects. In the wavelength conversion element, it is required to align the phases of the harmonic waves generated on the light path of the fundamental wave in order for improve the conversion efficiency. This phase matching includes birefringent phase matching utilizing birefringence of the nonlinear optical element and quasi-phase matching utilizing a cyclic polarization inversion structure. In the nonlinear optical element of recent years, the quasi-phase matching is often used because of an advantages that there is no limitation in the conversion wavelength and that the conversion efficiency is high, and of progress in the polarization inversion technology.
JP-A-6-160926 is an example of a related art document.
However, an appropriate polarization invention period is different in accordance with the wavelength of the fundamental wave, and the range of the fundamental wave which can be converted is very narrow. Since the wavelength of the fundamental wave has variations caused by the individual difference in the laser emitting element, and further, varies in accordance with the temperature of the laser emitting element or the environmental temperature, it is difficult to always match the phase of the fundamental wave with the conversion wavelength determined in accordance with the polarization inversion period. Therefore, in the laser source device using the nonlinear optical element, there is a problem that decrease in the wavelength conversion efficiency is caused by the mismatch between the conversion wavelength and the wavelength of the fundamental wave, which makes laser beam emission with stable output power difficult.
The problem mentioned above is not specific to the image display device, but is common to a monitor device or a lighting device equipped with the laser source device using the nonlinear optical element as the wavelength conversion element.